even Cyanobacteria (Chadefaud 1960; Lecointre and Le
Guyader 2006). According to Nozaki et al. (2009), they are
closer to Chromalveolata and Viridiplantae than to
Rhodobionta. Here, we have placed Glaucocystobionta
within the kingdom Archaeplastida (Palmer et al. 2004;
Yoon et al. 2006b; Leliaert et al. 2012), which is challenged
by some authors (e.g., Cuvelier et al. 2008). A dozen species
are known, belonging to the genera Cyanophora,
Glaucocystis, and Gloeochaete.
If the position of Glaucocystobionta in the phylogenetic
tree of eukaryotes, adopted here, is correct, they are of considerable theoretical interest. Their chloroplasts would testify
to the best preserved eukaryotic lineage which experienced
the primary endosymbiosis with a cyanobacterium and
allowed eukaryotes to acquire photosynthesis (cf. Sect. 5.4).
Glaucocystobionta are unicellular. The cell wall may be
present, and in this case consists of cellulose (Glaucocystis),
or absent (Cyanophora). Beneath the plasmalemma (cytoplasmic membrane), alveolae (alveolar sacs) similar to
those of the kingdom Alveolata are present (Fig. 7.13).
The chloroplast is much like a cyanobacterium; it has long
been regarded as a mutual cyanobacterium, insofar as the
peptidoglycan cell wall of Cyanobacteria is maintained
between the two chloroplast envelopes, a unique feature
in eukaryotes (Bhattacharya et al. 2003) (Fig. 7.13). If
chloroplasts are experimentally removed, the cell dies,
indicating that endosymbiosis is obligate. Within the chloroplast stroma, thylakoids* are isolated, as in Rhodobionta,
not stacked; they contain chlorophyll a; they bear
phycobilisomes, which contain two blue phycobilins
(phycocyanine and allophycocyanin), photosynthetic
pigments especially efficient at absorbing red, orange, yellow, and green light, wavelengths that are not well absorbed
by chlorophyll a. The polysaccharides arising from photosynthesis, mainly true starch, a mixture of amylose (an
Axopod
Mitochondrion
Nucleus
Siliceous scale
Microtubule
Centroplast
Fig. 7.11 Simplified and
theoretical scheme of a cell of
Centrohelida. Only part of the
organelles are shown
Fig. 7.12 Raphidiophrys pallida (Centrohelida). The axopods and
siliceous spicules are visible (From Gazzaniga (2009). Photograph:
courtesy of Maurizzio Gazzaniga)
208
C.-F. Boudouresque
Guyader 2006). According to Nozaki et al. (2009), they are
closer to Chromalveolata and Viridiplantae than to
Rhodobionta. Here, we have placed Glaucocystobionta
within the kingdom Archaeplastida (Palmer et al. 2004;
Yoon et al. 2006b; Leliaert et al. 2012), which is challenged
by some authors (e.g., Cuvelier et al. 2008). A dozen species
are known, belonging to the genera Cyanophora,
Glaucocystis, and Gloeochaete.
If the position of Glaucocystobionta in the phylogenetic
tree of eukaryotes, adopted here, is correct, they are of considerable theoretical interest. Their chloroplasts would testify
to the best preserved eukaryotic lineage which experienced
the primary endosymbiosis with a cyanobacterium and
allowed eukaryotes to acquire photosynthesis (cf. Sect. 5.4).
Glaucocystobionta are unicellular. The cell wall may be
present, and in this case consists of cellulose (Glaucocystis),
or absent (Cyanophora). Beneath the plasmalemma (cytoplasmic membrane), alveolae (alveolar sacs) similar to
those of the kingdom Alveolata are present (Fig. 7.13).
The chloroplast is much like a cyanobacterium; it has long
been regarded as a mutual cyanobacterium, insofar as the
peptidoglycan cell wall of Cyanobacteria is maintained
between the two chloroplast envelopes, a unique feature
in eukaryotes (Bhattacharya et al. 2003) (Fig. 7.13). If
chloroplasts are experimentally removed, the cell dies,
indicating that endosymbiosis is obligate. Within the chloroplast stroma, thylakoids* are isolated, as in Rhodobionta,
not stacked; they contain chlorophyll a; they bear
phycobilisomes, which contain two blue phycobilins
(phycocyanine and allophycocyanin), photosynthetic
pigments especially efficient at absorbing red, orange, yellow, and green light, wavelengths that are not well absorbed
by chlorophyll a. The polysaccharides arising from photosynthesis, mainly true starch, a mixture of amylose (an
Axopod
Mitochondrion
Nucleus
Siliceous scale
Microtubule
Centroplast
Fig. 7.11 Simplified and
theoretical scheme of a cell of
Centrohelida. Only part of the
organelles are shown
Fig. 7.12 Raphidiophrys pallida (Centrohelida). The axopods and
siliceous spicules are visible (From Gazzaniga (2009). Photograph:
courtesy of Maurizzio Gazzaniga)
208
C.-F. Boudouresque